Many researchers propose that high fat diets lead to obesity, which may in turn predispose individuals to the development of non-insulin dependent diabetes mellitus (NIDDM), dyslipidemia, hypertension and cardiovascular disease. Studies in animals and humans have shown that the fat content of the diet, and the type of fat, alters insulin action and energy metabolism. The type of fat consumed may also have adverse consequences on chronic disease states. Epidemiological and experimental studies have shown that dietary fat intake influences insulin action, although the mechanisms are not clearly defined. The ability of fatty acids to stimulate insulin secretion is a function of chain length and degree of saturation. The type of effect appears to be related to the fatty acid profile of the dietary fat. Fatty acid composition of the diet may also influence insulin sensitivity. At the cellular level, there appear to be differences in insulin binding and glucose transport in cells grown with different types of fat in the incubation medium. It is unclear what action saturated fat, monounsaturated fat, polyunsaturated fat or specific fatty acids have on fat oxidation. Human studies that examine the effect of feeding individual fatty acids on insulin secretion, insulin sensitivity, fat oxidation and whole body calorimetry are lacking. The purpose of this study is to determine the acute effects of feeding a high palmitic acid lipid, a high oleic lipid and a high linoleic lipid on insulin secretion, insulin sensitivity and fat oxidation. Our ultimate plan is to use the data obtained in this pilot study to study obesity, NIDDM and other chronic disease states.